Silver image stabilization with noble metal compounds

ABSTRACT

THE PRESENT INVENTION RELATES TO A PHOTOGRAPHIC SILVER DIFFUSION TRANSFER PROCESS WHICH COMPRISES, IN ESSENCE, EXPOSING A SILVER DIFFUSION TRANSFER FILM UNIT WHICH COMPRISES PHOTOSENSITIVE SILVER HALIDE AND SILVER PRECIPITATING NUCLEI; CONTACTING THE EXPOSED FILM UNIT WITH A PROCESSING COMPOSITION WHICH COMPRISES A SILVER HALIDE DEVELOPING AGENT AND A SILVER HALIDE SOLVENT TO PROVIDE A VISIBLE SILVER IMAGE TO THE UNIT, AS A FUNCTION OF EXPOSURE; AND COACTING THE SILVER IMAGE WITH A NOBLE BELOW SILVER IN THE ELECTROMOTIVE FORCE SERIES OF ELEMENTS AT A CONCENTRATION EFFECTIVE TO ENHANCE STABILITY OF A SILVER IMAGE PROVIDED BY DIFFUSION TRANSFER PROCESSING OF THE FILM UNIT.

NOV. 28, 1972 LAND ETAL 3,104,126

snmaa IMAGE STABILIZATION WITH NOBLE METAL courouuns Fi Ied- Dec. 7.1970 1 2 Sheets-Sheet 1 0F ORIGINAL DENSITY DAYS (1.0a SCALE) FIGI Nov.28, 1972 LAND U'AL 3,704,126

SILVER IMAGE STABILIZATION WITH NOBLE METAL COMPOUNDS Filed Dec. 7, 19702 Sheets-Sheet, 2

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INVENTORS ggwn H.LAND s NL Y M. BLOOM and BY LEONARD C.FARNEY E/zawn w7% ATTORNEYS United States Patent O 3,704,126 SILVER IMAGE STABILIZATKONWITH NOBLE METAL COMPOUNDS Edwin H. Land, Cambridge, Stanley M. Bloom,Waban, and Leonard C. Farney, Melrose, Mass, assignars to PolaroidCorporation, Cambridge, Mass.

Filed Dec. 7, 1970, Ser. No. 95,424 Int. Cl. G03c 5/54 U.S. CI. 96-29 R56 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to aphotographic silver diffusion transfer process which comprises, inessence, exposing a silver diffusion transfer film unit which comprisesphotosensitive silver halide and silver precipitating nuclei; contactingthe exposed film unit with a processing composition which comprises asilver halide developing agent and a silver halide solvent to provide avisible silver image to the unit, as a function of exposure; andcoacting the silver image with a noble metal below silver in therElectromotive Force Series of Elements at a concentra tion effective toenhance stability of a silver image provided by diffusion transferprocessing of the film unit.

BACKGROUND OF THE INVENTION (1) Field of the invention The presentinvention is directed to providing a new and improved silver andadditive color diffusion transfer photographic process which ispreferably adapted to provide, as a function of the point-to-pointdegree of photoexposure, composite integral negative and positivephotographic silver images which include a negative silver image insuperposed relationship with a positive silver image.

(2) Description of prior art As disclosed in U.S. Pat. No. 2,861,885,desirable composite prints comprising both negative and positive imagesin superposition may be provided by a silver diffusion transfer reversalprocess employing a photosensitive silver halide emulsion which uponsubstantially full development of its exposed areas, as a function ofexposure, provides a relatively low maximum density negative silverimage with relation to the high maxi-mum density positive silver imageprovided by a silver precipitating environment of the type detailedbelow. In a composite print produced in accordance with the disclosureof the cited patent, the covering power of a given mass of image silverin the print-receiving element is there stated to range from 14 to 15times that of an equal mass of image silver in the silver halide elementand, that for transparency employment, a maximum negative density of ashigh as 1.0 density units may be permissible where the maximum positivedensity is about four or more times as great.

The image-receiving element so employed is disclosed to be constitutedas to provide an unusually effective silver precipitating environmentwhich causes the silver deposited therein, in comparison with negativesilver developed in the silver halide layer, to possess anextraordinarily high covering power, that is, opacity per given mass ofreduced silver; see Edwin H. Land, One Step Photography, PhotographicJournal, Section A., pp. 7-115, January 1950.

Specifically, to provide such environment, silver precipitation nucleiare disclosed to be disposed within the silver receptive stratum inclusters possessing a diameter directly proportional to the mass ofimage silver to be deposited in situ by reduction. Such conformation isemployed to cause image silver to precipitate, in association 3,704,126Patented Nov. 28, 1972 ice with the silver precipitation nucleiclusters, with the required density and of a size directly related tothe physical parameters of the clusters and the image silver thusprecipitated, in situ, in galaxies of chosen physical parameters toprovide image conformation in which the ele mental silver of theimage-receiving element may possess a very high order of covering power,for example, five to fifteen or more times that of the negative imagesilver in the silver halide layer.

In accordance with the disclosures of U.S. Pats. Nos. 2,726,154 and2,944,894 additive multicolor reproduction may be accomplished by adiffusion transfer reversal process which specifically includes exposureof an integral multilayer film assemblage through an optical screencomprising a plurality of minute optical elements and carryingphotosensitive and image-receptive layers. As disclosed, diffusiontransfer processing may be accomplished by permeation of thephotoexposed integral film unit with a fluid processing composition andthe image-receptive layer retained in permanent fixed relationship tothe screen during and subsequent to, formation of the requisite transferimage, with the operators option of separating the photosensitive layerfrom the remainder of the film unit, subsequent to transfer imageformation, in film unit structures possessing the imagereceiving layerintermediate the screen and emulsion components.

Integral additive color diffusion transfer film assemblages, essentiallycomprising photoresponsive material directly providing positive imageformation and possessing the sensitivity to incident electromagneticradiation and acuity of image formation necessary to effectively providecolor photographic image reproduction, are disclosed and claimed in thefollowing copending applications, which are directed, in general, tofilm unit assemblages which comprise a permanently fixed laminateincluding a support carrying on one surface an additive color screen,photosensitive silver halide and silver precipitating nuclei:

Application Ser. No.: Filing date 736,796 June 13, 1969. 889,656 Dec.31, 1969. 889,657 Dec. 31, 1969. 889,660 Dec. 31, 1969. 889,636 Dec. 31,1969.

now U.S. Pat. No. 3,536,488 issued Oct. 27, 1970 and U.S. Pats. Nos.3,615,427; 3,615,428; 3,615,429; and 3,615,426, all issued Oct. 26,1971, respectively. The aforementioned applications are incorporated byreference herein in their entirety.

In the above-indicated film assemblages the silver precipitating nucleiare present in a concentration effective to provide a silve image to thefilm unit possessing optical density inversely proportional to exposureof the photosensitive silver halide layer, and specifically, in aconcentration adapted to provide a silver image derived from unexposedsilver halide crystals possessing greater covering power than that ofcorresponding silver image derived from identical quantum of exposedsilver halide crystals.

As set forth in the above-indicated applications, improved imagereproduction may be obtained by means of the improved silver imagecharacteristics provided therein. Specifically, the above-indicatedapplications state that composite negative/ positive silver imageformation possessing an optical density inversely proportional tophotoexposure of a photosensitive silver halide layer, characterized byimproved silver image minimum and maximum optical densities and imageacuity may be achieved by a process which includes exposing aphotographic film unit, which comprises a permanent laminate containinga support carrying on one surface silver precipitating nuclei andphotosensitive silver halide, and processing the film unit by contact,simultaneous with, or subsequent to, exposure, with an aqueousprocessing composition, containing a silver halide developing agent anda silver halide solvent, to provide to the film unit the directformation of a silver image possessing particularly desired low minimumsilver image optical density, in terms of exposed areas of the filmunit, and high maximum silver image optical density, in terms ofunexposed areas of the film unit, as a function of exposure anddevelopment of the film unit.

The above-mentioned film units are disclosed to be particularlydesirable for employment as a cine film for motion picture projection byreason of the inherent ability to simply and effectively process such afilm, employing relatively simple and stable processing compositions,without the necessity of providing a process and apparatus specificallyadapted to effect stripping of a separate emulsion stratum from theremainder of the film unit to pro vide information recordationpossessing the image integrity in reproduction characteristics requiredfor effective employment of the film.

Such film assemblages are suitably employed in a cine film system suchas that described in application Ser. No. 755,901, filed Aug. 28, 1968,now US. Pat. No. 3,615,127 issued Oct. 26, 1971, which includes acompact cine film cassette or container adapted to allow exposure of afilm assemblage as retained therein, subsequent processing of the filmto provide the desired image record and projection of the resultantimage record or other presentation for viewing purposes. Thus, the filmassemblage may be exposed, processed, dried if necessary, and projectedwithout transferring the film from its original container to any othercontainer or even in elfect removing the film from the originalcontainer. The cine film system of application Ser. No. 755,901, US.Pat. No. 3,615,127, includes a film processing station whereupon theexposed film strip is transported from a first storage reel, past anapplicator where a moist processing composition to develop to a visiblecondition images recorded on the film is applied and thence to a secondstorage reel.

The processing composition may be applied to the film assemblage by avariety of methods such as, for example, doctor blades, extrusion heads,capillary applicators, wicks, and the like. The amount of processingcomposition applied to the assemblage should be controlled withinrelatively narrow limits, however, sufiicient processing compositionmust be applied to adequately and completely permeate the assemblage tothe depth necessary and in the quantity necessary to provide the desiredimage conformation.

The processing composition employed will generally include an alkalinematerial, for example, sodium hydroxide, potassium hydroxide, sodiumcarbonate, or the like, and most preferably, in a concentrationproviding a pH to the processing composition in excess of about 12. Theprocessing composition may, if desired, contain the sole silver halidedeveloping agent or agents and/or solvent or solvents employed or silverhalide developing agent and/or solvent in addition to that disposed asin the film unit. The relative proportions of the agents comprising thedeveloping composition may be altered to suit the requirements of theoperator. Thus, the developing composition may be modified by theemployment of preservatives, alkalis, silver halide solvents, etc.,other than those specifically mentioned herein. When desirable it isalso contemplated to include in the developing composition componentssuch as restrainers, accelerators, and the like, and the concentrationof such agents may be varied over relatively wide range commensuratewith the art.

In the film units and processes set forth in the above- 4 indicated U.S.Pats. Nos. 2,726,154 and 2,944,894, and the above-indicated copendingapplications, a quantity of processing composition and reactants willinevitably be retained within the film unit, particularly if theimagereceiving layer is maintained in permanent relationship with theemulsion as well as the screen, and this residuum may possess thecapacity to deleteriously effect image quality over an extended periodof time, in addition to conventional environmental degradation of imagesilver.

SUMMARY OF THE INVENTION The present invention is specifically directedto a novel photographic silver diffusion transfer process uniquelyadapted to provide silver transfer images possessing image stability inexcess of that provided by prior art processes and Which processcomprises, in essence, exposing, to incident actinic radiation, a silverdiffusion transfer film unit which includes photosensitive silver halideand silver precipitating nuclei; contacting the exposed film unit with aprocessing composition comprising a silver halide developing agent and asilver halide solvent to provide a visible silver image to the unit, asa function of the pointto-point degree of exposure thereof; and coactingthe silver image with a noble metal below silver in the ElectromotiveForce Series of Elements, at a concentration effective to enhance thestability of silver image provided by diffusion transfer processing ofthe unit.

The silver diffusion transfer process of the invention is specificallyadapted to provide silver diffusion transfer images exhibiting improvedstability with respect to degradative attack by film unit retainedresidual processing reagents and environmental image contaminants.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphic illustration ofthe stability characteristics of a silver diffusion transfer imageprepared in accordance with the present invention, compared with acorresponding control silver transfer image of the prior art, determinedby plotting comparative silver transfer image density loss in percent,under the stated test conditions, as a function of time; and

FIG. 2 is a graphic illustration of the characteristic curves of asilver transfer image of the present invention, compared with acorresponding prior art control, determined by plotting the density ofthe transfer image to blue, green and red light as a function of the logexposure of the photosensitive silver halide emulsion component of thefilm units employed.

DETAILED DESCRIPTION OF THE INVENTION As previously characterized, asilver diffusion transfer process may be employed to provide a silvertransfer image, which. may comprise an integral negative silver image insuperposed relationship to a positive silver image adapted to exhibitgreater covering power than the negative image, by development of thelatent image provided a photosensitive silver halide element by exposureand, substantially contemporaneous with such development, formation of asoluble silver complex by reaction of a silver halide solvent withunexposed and undeveloped silver halide of the element. The silver ofthe resultant soluble silver complex is, at least in part, precipitatedin the presence of silver precipitating nuclei to provide the requisitepositive silver image formation, which may optionally be retained incontiguous relationship to a negative silver image resultant fromdevelopment of the latent image carried by exposed silver halide and theconcomitant reduction of exposed silver halide to negative 1mage silver,or separated therefrom subsequent to substantial transfer imageformation.

In accordance with the present invention, a substantially enhanceddegree of stability may be imparted to the silver transfer image bycoacting transfer image silver with a noble metal below silver in theElectromotive 'Force Series of Elements at a concentration effective toenhance the stability of the silver image provided by diffusion transferprocessing of a silver diffusion transfer film unit.

The noble metal may be provided to the silver transfer image by theemployment of a noble metal donor compound which is preferably solublein the processing composition selected to effect the diffusion transferprocess, but which when predisposed in the film unit for solubilizationby the composition is substantially insoluble in the film unit mediumwithin which it is disposed during storage and most preferably issolubilized at a rate particularly adapted to avoid deleteriousinteraction during the initial stage in the development of latent imageimpressed upon the film units silver halide by photoexposure.Commensurate with the employment of conventional alkaline processingcompositions and the substantially neutral pH environment of silverdiffusion transfer film unit sheet elements in general employment, thepreferred noble metal donors for distribution within such sheet elementswill comprise substantially waterinsoluble, alkaline processingcomposition soluble noble metal donors.

In the practice of the present invention, the noble metal donor maycomprise inorganic and organic noble metal compounds and in thepreferred embodiments of the invention will comprise an organometalcompound which is substantially water-insoluble, alkaline solutionsoluble and may specifically comprise a compound of the formula:

wherein M is a noble metal less reactive than silver, i.e., below silverin the Electromotive Force Series of Elements and X is an organiccomplexing ligand which in the preferred embodiments of the inventionprovides a substantially water insoluble complex.

The noble metals required are those less reactive than silver, that is,those below silver in the Electromotive Force Series of Elements,preferably, palladium, platinum and gold and most preferably Au+ and Au+The particular organic ligand preferably selected will be one which willstrongly bond to both the noble metal ion with which it is initiallyassociated and also silver ion displaced from the positive image, shouldimpart a relatively low degree of water solubility to the complex andmust not deleteriously interfere with the photographic utility of thefilm unit.

As will be further described in specific detail below, and subject tothe criteria set forth herein, the selected noble metal compound may bedisposed in various locations in the film unit such as, for example, inthe photosensitive layer, in the image-receiving layer, in a separatelayer, or in the processing composition, recognizing that the cmopoundmust be selected to avoid any deleterious sensitometric effect to thefilm unit or interference with positive silver image formation, and mustbe stable in the particular environment in which it is disposed, e.g.,in an alkaline processing composition medium.

In a particularly preferred embodiment of the present invention, anorganic ligand is selected which is a sulfur containing moiety sincesuch ligands possess a specifically desired affinity for noble metalions. Particularly preferred such ligands are sulfur atom containingheterocyclic moieties which form stable, substantially water-in solubleorganometal compounds with noble metals, and particularly those ligandswhich possess a preferential affinity for silver ions.

As examples of ligands contemplated for employment in the practice ofthe present invention, mention may be made of:

Z-mercaptobenzimidazole, 2-mercaptoacetamidothiadiazole,Z-mercapto-N-methylimidazole, Z-mercaptobenzothiazole,

6 Z-mercaptobenzoxazole, 1- 3 ,5 '-dicarboxyphenyl -5-mercaptotetrazole,1-phenyl-S-mercaptotetrazole, 2-mercaptobenzselenazole, phenanthroline,2,2-dipyridyl, 8-aminoquinoline,

and the like.

In general, it has been found that a water-insoluble noble metalcompound employed in accordance with the present invention may be addedto the film unit at any stage during its manufacture and/or duringphotographic processing of same. The addition, therefor, may be madebefore, during or subsequent to fabrication and/or processing of thefilm unit although, as stated herein, the compound will preferably beadded as a coating final to, for example, the photosensitive silverhalide coating solution prior to its application to a supporting member.It will be recognized that the noble metal employed in accordance withthe invention may also be utilized in combination with additional knownimage modifying adjuvants such as toning agents, and the like, Wheredesired.

As examples of noble metal compounds, contemplated for employment in thepractice of the present invention, mention may be made of organometalcompounds such as, for example, gold mercaptobenzimidazole, goldmercaptoacetimidothiadiazole, gold mercapto N methylimidazole, goldphenylmercaptotetrazole, etc., and inorganic noble metal compounds suchas, for example,

gold thiourea, gold thiocyanate, gold chloride, sodium chlorolaurate,etc., and corresponding platinum, palladium, and the like, noble metalanalogues.

In general, the optimum concentration of noble metal to be employedshould be determined empirically for each specific photographic filmunit system. However, it has been determined that, in general, thepreferred concentration to be utilized based upon noble metal will fallwithin the range of about 1% to 20% of the silver present in thephotosensitive silver halide layer.

Although concentrations in excess of the stated range may be employed,increasing the concentration beyond the designated limits generallyprovides no commensurate beneficial results. Conversely, concentrationsbelow that of the designated range, however, merely decreasestabilization of the resultant silver transfer image below thebeneficial level generally sought, but does not obliterate obtainingbeneficial stabilization results.

In point of fact, advantageous results are obtained employing minimalconcentrations of noble metal adapted to provide a metal interchangewith minimal quantities of elemental image silver.

While not intending to be bound by theory, it is believed that partialreplacement of elemental image silver by the selected noble metalprovides a decrease in the reactivity of the image silver with respectto interaction with degradative materials provided by residualprocessing reagent present in the film unit or the environment.Specifically, in the preferred embodiments of the invention silver ionsderived from image silver may be displaced by noble metal ions derivedfrom a selected compound by a redox reaction resulting in the generationof noble metal and bound silver ions thus providing to at least aportion of the silver image a less reactive component.

As stated above, the noble metal donor may be disposed in a variety oflocations in the film unit. Suitable film units include, but are notlimited to those set forth in, the aforementioned U.S. Pats. Nos.3,536,488; 3,615,427; 3,615,428; 3,615,429; and 3,615,426. Thus, thepresent invention includes film units comprising a photosensitive silverhalide layer and a silver precipitating nuclei containingimage-receiving layer adapted to provide positive silver image formationin the reception layer by diffusion transfer processing, which theimage-receiving layer may be maintained in superposed relationship withthe negative image or separated therefrom, and film units which comprisestructures adapted to provide direct positive silver image formationsuch as, for example, film units possessing silver precipitating nucleidirectly associated with photosensitive silver halide.

As will be readily recognized, additional layers may be optionallyincluded in the film unit such as, for example, a separate layerretaining the noble metal donor of the present invention as well asspacer layers, barrier layers, protective layers, stripping layers, andsupport layers.

In the preferred embodiment of the present invention the film unitcomprises a support preferably transparent to actinic radiation andcarrying on a first surface a photosensitive silver halide layer and alayer containing silver precipitating nuclei dispersed therein and, forcolor image reproduction, an additive color screen is interposed betweenthe transparent support and the photosensitive silver halide layer.

Employment of the preferred organometal complexes or compounds whereinthe organic ligand is a sulfur containing heterocyclic ligand of thetype which acts as a silver halide photographic stabilizing agent mayeffectively enhance storage stability of the film unit in which thecomplex is disposed. Thus, rather than inducing deleterious effects tothe film in which it is disposed, the noble metal complex mayadditionally provide resistance to the normal storage fog degradationgenerally encountered in silver halide emulsions.

As will be readily recognized, the metal donor may also be located inwhole or in part in a separate layer in the film unit, preferablyadjacent to the layer in which the image silver is to be located;directly in the image-receiving layer and associated with the silverprecipitating nuclei, or in the liquid processing composition, and aplurality of donors may be optionally employed, which donors may bedisposed, individually or in combination, at one or more of suchlocations. .As stated above, in the instance that donor is disposed inthe processing composition, the specific organic ligand should beselected to avoid any degradative effects which may occur during storagein the specific media of the processing composition, generally a highlyalkaline medium. In instances where is is desired to distribute a noblemetal donor to the silver image by means of a processing composition inwhich it fails to exhibit required storage stability, the donor may beinitially disposed in association with a selected processing compositionapplicator such that it is solubilized by and incorporated in thecomposition immediately preceding, or during, application of thecomposition to the film unit as, for example, initially disposed in aprocessing composition applicator wick which provides the transportconduit between the storage chamber for the composition and the filmunit during processing.

In addition to the above-mentioned stabilization properties, that is,stabilization of silver image quality and re sistance to degradation ofthe silver image from residual reagent and atmospheric contact, it hasalso been discovered that visual image quality with respect to toningmay be achieved such as to provide a blacker or more neutral silverimage.

In a plurality of the above-described film units, the negative silver isalso available fo inteaction with the noble metal, particularly where anintegral unit is employed or where the metal donor is initially disposedin the photosensitive silver halide layer. In such units, although theentire amount of silver initially in the unit remains present,

in composite film unit structures the negative silver is not visuallypresent to the observer by reason of the difference in covering powerand physical state between the respective positive image silver and thenegative image silver. It is believed that by reason of, for example,covering'power and physical state, including surface area of individualimage silver particles, the present invention is preferentiallyeffective with respect to effecting stabilization of the desiredpositive transfer silver image possessing the physical characterdescribed above, without appreciable deleterious effect with respect tothe covering power of either the negative or the positive silver image.In addition, it is understood that negative image may act as adeposition matrix to effect removal, from the active photographicsystem, of noble metal in excess of that required to effectstabilization of the positive silver image.

Although as previously stated, a specifically preferred noble metalcomprises gold, it has been found that the employment of the statedmetal does not result in the deposition of red gold contaminating imageintegrity. Thus, the photographic quality of the image is not impairedby extraneous reactions of the preferred metal and the gold componenthas not been found to deposit on, or to interfere with, the operation ofconventional silver transfer image nucleating sites.

In the practice of the present invention, the silver precipitatingnuclei may be disposed within the photosensitive silver halide stratumof the film unit assemblages, in a separate layer or layers or elementcontiguous one or both surfaces of the silver halide stratum and thesilver halide stratum may comprise two or more silver halide strata,each optionally retaining silver precipitating nuclei, and may include aseparate silver precipitating nuclei layer positioned intermediateseparate silver halide strata.

For the purpose of insuring the production of a positive imagepossessing a high covering power, the silver precipitating nuclei willbe disposed within the film unit in a concentration per unit areaeffective to cause image silver derived from unexposed silver halidecrystals to possess the desired opacity per given mass of in situreduced silver.

In general, silver precipitating nuclei comprise a specific class ofadjuncts well known in the art as adapted to effect catalytic reductionof solubilized silver halide specifically including heavy metals andheavy metal compounds such as the metals of Groups I-B, II-B, IVA, VIA,and VIII and the reaction products of Groups I-B, II-B, IV-A, and VIIImetals with elements of Group VI-A, and may be effectively employed inthe conventional concentrations traditionally employed in the art,preferably in a relatively low concentration in the order of about l-251O- moles/ftf".

Especially suitable as silver precipitating agents are those disclosedin US. Pat. No. 2,698,237 and specifically the metallic sulfides andselenides, there detailed, these terms being understood to include theselenosulfides, the polysulfides, and the polyselenides. Preferred inthis group are the so-called heavy metal sulfides. For best results itis preferred to employ sulfides whose solubility products in an aqueousmedium at approximately 20 C. vary between 10- and lO and especially thesalts of zinc, copper, cadmium and lead. Also particularly suitable asprecipitating agents are heavy metals such as silver, gold, platinum,palladium, etc., and in this category the noble metals illustrated arepreferred and are generally provided in the matrix as colloidalparticles.

In particular, it has been discovered that improved color reproductionin accordance with the principles of additive color photography may beobtained by means of the improved image characteristics provided byreason of the present invention. Specifically, it has been found thatcomposite negative/positive silver image formation, particularly adaptedfor additive color reproduction and characterized by improved silverimage minimum and maximum optical densities and image acuity may beachieved by a process which includes exposing a photographic film unit,which comprises a color screen in association with a photosensitivesilver halide layer fabricated to conform to the parameters previouslyset forth and having associated therewith silver precipitating nucleiwherein the exposure of the emulsion is effected by radiation traversingthrough the color screen and the processing of the film is accomplishedby contact, simultaneous with, or subsequent to, exposure, with anaqueous processing composition, containing a silver halide developingagent and a silver halide solvent, to provide to the film unit thedirect formation of a silver image possessing required low silver imageoptical density, in terms of exposed areas of the film unit, andrequired high silver image optical density, in terms of unexposed areasof the film unit, as a function of exposure and development of the filmunit.

Color photographic reproduction may thus be provided by exposing theabove described photoresponsive silver halide stratum, to selectedsubject matter, through an optical screen element possessing filtermedia or screen elements of selected radiation modulatingcharacteristics such as filter media selectively transmittingpredetermined portions of the electromagnetic radiation spectrumsvisible segment. The color information thus recorded is read out byviewing resultant image conformation through the same or a similarscreen element in appropriate registration with the image. Theindividual filter media or screen elements constituting the opticalscreen will be constructed to effect selective filtration ofpredetermined portions of the visible electromagnetic spectrumsubstantially corresponding to its red, blue and green regions and colorinformation recordation will be accomplished by point-topoint incidenceof radiation actinic to the selected photoresponsive material asmodulated by such screen element. Visual reproduction of the informationcontent recorded is accomplished by read out of the impressed image asmodulated by the original or a substantially identical screen element inaccurate registration with the image record.

Although for color information recordation purposes, the photoresponsivematerial and optical screen may comprise separate and distinct elementsappropriately registered during periods of exposure and viewing and theoptical screen element may be temporarily or permanently positioned onthe surface of a transparent carrier opposite that retaining thephotoresponsive material, for practical purposes, it is preferred topermanently position the photoresponsive material in direct contiguousrelationship to the color screen during exposure, in order to maximizethe acuity of the resultant image record.

Subsequent to exposure of the photoresponsive material to actinicradiation transmitted through and filtered by the optical screen, theresultant photoexposed element may be further processed in accordancewith the materials selected and generally without regard to the filterscreen when the latter element is stable with respect to and/orprotected from contact with the processing compositions and componentsselected. Such protection and stability will ordinarily be enhanced andfacilitated by disposition of the filter screen between a transparent,processing composition impermeable carrier and the photoresponsivematerial, and, in particular, where such configuration additionallyincludes the presence of a processing composition barrier element orlayer intermediate the screen and the photoresponsive material.

The preferred film assemblages will comprise a panchromaticallysensitized silver halide stratum possessing the parameters previouslyset forth positioned contiguous a surface of the multicolor additivecolor screen Which, in the preferred assemblage denoted above, may alsopossess the image-receiving component intermediate a silver halidestratum and the color screen, to allow exposure of the emulsion to beaccomplished through a color screen, including through a transparentsupporting member, if present, and formation of the requisite positivesilver image in immediate, contiguous relationship to the color screenemployed during exposure. Such embodiment obviates the necessity ofregistering the color screen with the resultant positive silver image,for viewing purposes, in that the screen employed for exposing may alsobe employed for viewing and is in automatic registration with thepositive silver image.

Thus a preferred embodiment of the present invention for thereproduction of color information in accordance with the principles ofadditive color photography may comprise a film unit assemblage whichcontains an additive multicolor screen comprising a geometricallyrepetitive plurality of actinic radiation-filtering colored elementsincluding a set of primary blue-colored filtered elements, a set ofprimary green-colored filter elements and a set of primary red-coloredfilter elements arranged in a repetitive distribution in side-by-siderelationship in a substantially single plane positioned intermediate atransparent support member and a photosensitive silver halide stratumconforming to the parameters set forth above and having silverprecipitating nuclei associated therewith in any of the mannerspreviously detailed.

It will be specifically recognized, however, that in embodiments of theinvention which employ a separate photosensitive silver precipitatingnuclei containing layer, intermediate a color screen and aphotosensitive silver halide layer, such nuclei containing layer shouldmost perfera-bly possess a thickness of less than about a wavelength oflight so that for all practical optical purposes the photosensitivesilver halide emulsion layer will be effectively located next adjacentthe color screen whereby minimizing to a maximum extent any possibleoptical parallex problems during radiation transmission, as well as anysubstantial lateral diffusion of silver imageforming components duringprocessing of the film unit.

The photoresponsive silver halide materials employed in the practice ofthe present invention will, as previously described, comprise a crystalof a compound of silver, for example, one or more of the silver halides,such as photosensitive silver chloride, silver iodide, silver bro mide,and preferably, mixed silver halides, such as silver chlorobromide,silver iodochloride, silver iodobromide or silver iodochlorobromide, ofvarying halides ratios and the silver concentrations dispersed in aprocessing composition permeable binder material such as gelatin and thelike, most preferably silver iodobromide and iodochlorobromide,particularly that comprising -1 to 9% iodide by weight of silver.

The preferred silver halide type photosensitive layers employed for thefabrication of the photographic film unit, may be prepared by reacting awater-soluble silver halide, such as ammonium, potassium or sodiumchloride, preferably together with corresponding iodide and bromide, inan aqueous solution of a peptizing agent such as colloidal gelationsolution; digesting the dispersion at an elevated temperature, toprovide increased crystal growth; washing the resultant dispersion toremove undesirable reaction products and residual watersoluble salts,for example, employing the preferred gelatin matrix material, bychilling the dispersion, noodling the set dispersion, and washing thenoodles with cold water, or, alternatively, employing any of the variousfloc systems, or procedures, adapted to effect removal of undesiredcomponents, for example, the procedures described in US Pats. Nos.2,614,928; 2,614,929; 2,728,- 662, and the like; after ripening thedispersion at an elevated temperature in combination with the additionof gelatin or such other polymeric material as may be desired andvarious adjuncts, for example, chemical sensitizing agents and the like;all according to the traditional procedures of the art, as described inNeblette, C. B., Photography--Its Materials and Processes, 6th ed.,1962.

Optical sensitization and preferably panchromatic sensitization of theemulsions silver halide crystals may then be accomplished by contactwith optical sensitizing dye or dyes; all according to the traditionalprocedures of the art, or described in Hamer, F. M. The Cyanine Dyes andRelated Compounds.

Subsequent to optical sensitization, any further desired additives, suchas coating aids and the like, may be incorporated in the emulsion andthe mixture coated according to the conventional photographic emulsioncoating procedures known in the art.

As the binder for the photoresponsive material, the aforementionedgelatin may be, in whole or in part, replaced with some other naturaland/or synthetic processing composition permea'ble polymeric materialsuch as albumin; casein; or zein or resins such as cellulose derivative,as described in U.S. Pats. Nos. 2,322,085 and 2,541,474; vinyl polymericsuch as described in an extensive multiplicity of readily available U.S.and foreign patents or the photoresponsive material may be presentsubstantially free of interstitial binding agent as described in U.S.Pats. Nos. 2,945,771; 3,145,566; 3,142,- 567; Newman, Comment onNon-Gelatin Film, B. J. O. P., 434, Sept. 15, 1961; and Belgian Pats.Nos. 642,557 and 642,558.

One procedure particularly useful for the production of one preferredgelatino silver halide emulsion comprises to formulation, in the mannerpreviously detailed, of a silver iodochlorobromide emulsion containingin order -1% iodide by initially forming a silver chloride emulsion,adding to the emulsion the requisite bromide and iodide, separating fromthe formulation undesired reaction products, and after-ripening theresultant silver iodochlorobromide emulsion in combination with theselected auxiliary sensitizing, speed increasing, etc., adjunctselected.

Specifically, the specified emulsion may be formulated by a conventionaldouble jet addition, over a period of 3 minutes and 25 seconds, at arate of 1800 cc. per minute of 1026 gms. of potassium chloride in 5336gms. of distilled water at 60 C. to a solution at 80 C. comprising 205gms. of potassium chloride, 5750 gms. of distilled water and 2560 gms.of a solution formed by dissolving 800 gms. of gelatin in 8800 mls. ofdistilled Water, adjusting the pH to :01 with 50% sodium hydroxide,adding over a 30 minute period and at 40 C. with stirring 88 gms. ofphthalic anhydride in 616 mls. of acetone, and after 30 minutes at 40 C.adjusting the pH to 6 with 50% sulfuric acid. After a digestion periodof 5 minutes at 80 C., 60 gms. of potassium iodide and 1337 gms. ofpotassium bromide in 5336 gms. of water is added to the formulation,over a period of 3 minutes and 25 seconds, at a rate of 1800 cc. perminute and at 60 C. and the resultant emulsion digested for a furtherperiod of 35 minutes at 80 C. The resultant silver iodochlorobromideemulsion is precipitated at C. by reduction of the pH to about 2.7 withsulfuric acid, the precipitate separated from the supernatant liquid andwashed with chilled distilled water until the wash water exhibits aconductivity of -50 to 100 rnhos/cm, the volume adjusted with distilledwater for the addition of 950 gms. of gelatin, and the emulsion thenafter ripening for 210 minutes at a temperature of 54 C. and a pH of5.7.

The silver precipitating nuclei and/or discrete nuclei layer or layersmay be realized by the application of, location of, and/or in situgeneration of, the nuclei, which may be similar or dissimilar, directlyor indirectly in or as the respective layer and in the presence orabsence of binder or matrix material and, in the latter instance, maycomprise one or more adjacent or separate strata of a permeable materialcontaining one or more nuclei types disposed in one or more such layers.Matrix materials adapted to such employment may comprise both inorganicand organic materials, the latter type preferably comprising natural orsynthetic, processing composition permeable, polymeric materials such asprotein materials, for example, glues, gelatins, caseins, etc.;carbohydrate materials,

for example, chitins, gums, starches, alginates, etc.; syntheticpolymeric materials, for example, of the vinyl or cellulosic types suchas vinyl alcohols, amides and acrylamides, regenerated celluloses andcellulose ether and esters, polyamides and esters, etc., and the like;and the former type preferably comprising submacroscopic agglomerates ofminute particles of a water-insoluble, inorganic, preferably siliceousmaterial such, for example, as silica aerogel as disclosed in U.S. Pat.No. 2,698,237.

Where the silver precipitating agent is one or more of the heavy metalsulfides or selenides, it may be preferable to prevent the diffusion andwandering of the sulfide or selenide ions, as the case may be, by alsoincluding, in the silver precipitating layers or in separate layersclosely adjacent thereto, at least one metallic salt which issubstantially more soluble in the processing agent than the heavy metalsulfide or selenide used as the silver precipitating agent and which isirreducible in the processing agent. This more soluble salt has, as itscation, a metal whose ion forms sulfides or selenides which aredifiicultly soluble in the processing agent and which give up theirsulfide or selenide ions to silver by displacement. Accordingly, in thepresence of sulfide or selenide ions the metal ions of the more solublesalts have the effect of immediately precipitating the sulfide orselenide ions from solution. These more soluble or ion-capturing saltsmay be soluble salts of any of the following metals: cadmium,cerium(ous), cobalt(ous), iron, lead, nickel, manganese, thorium andtin. Satisfactory soluble and stable salts of the above metals may befound, for example, among the following groups of salts: the acetates,the nitrates, the borates, the chlorides, the sulfates, the hydroxides,the formates, the citrates and the dithionates, The acetates andnitrates of zinc, cadmium, nickel, and lead are preferred. In general,it is also preferable to use the white or lightly colored salts althoughfor certain special purposes the more darkly colored salts may beemployed.

The previously mentioned ion-capturing salts may also serve a functionof improving the stability of the positive image provided they possess,in addition to the aforementioned characteristics, the requisitesspecified in U.S. Pat. No. 2,584,030. For example, if the ion-capturingsalt is a salt of metal which slowly forms insoluble or slightly solublemetallic hydroxides with the hydroxyl ions in the alkaline processingliquid, it will suitably control the alkalinity of the film unit tosubstantially, if not totally, prevent the formation of undesirabledeveloper stains.

In accordance with a particularly preferred embodiment of the presentinvention, photosensitive and imagereceiving strata carrying the imagesilver are fabricated to substantially prevent microscopic distortion ofthe image conformation by preventing microscopic migration or diffusionof image elements within the polymerix matrix. In general, conventionalphotographic image elements may ordinarily compirse a microscopicallydynamic system without seriously noticeable disadvantages to theconventional employment of the image. However, for particularly accuratecolor reproduction in accordance with the principles of additive colorphotography, microscopic distortion of image elements is preferablyobviated to insure maximization of the accuracy of image registrationwith the appropriate individual optical filter elements of the additivecolor screen associated with the image-carrying element. Specifically,it has been found that a photosensitive film unit comprisingphotosensitive emulsion containing silver halide crystals and silverprecipitating nuclei dispersed in a polymeric binder and where employedphotoinsensitive image-receiving layers containing silver precipitatingnuclei dispersed in a polymeric hinder, the binders of which possess alattice effective to substantially prevent microscopic migration ordiffusion of image silver, provide color reproduction acuityparticularly desired for effective color reproduction in the mannerpreviously described.

The desired polymeric binder lattice property may be readily achieved byselection of a polymeric material possessing the property ofsufficiently fixing spacially image components, or a polymeric material,otherwise desired, may be modified, for example, by crosslinking and/orhardening, to the extent necessary to provide the desired spacialmaintenance of image components, that is, a rigidity effective tomaintain positive image components in registration with the individualoptical filter elements of the color screen through which thephotosensitive emulsion was exposed. For example, a preferred polymericbinder material, that is, gelatin, may be hardened by contact withconventional hardening agents to the extent necessary to provide thedesired rigidification of the photographic image. Where desired discreteparticulate materials facilitating increased processing compositionpenetration of the photosensitive element, without deleterious effect onthe polymeric matrixs lattice, may be advantageously incorporated in thephotosensitive element for the purpose of expediting processing of theelement.

Production of color screen, in accordance with the art may be preparedby totally mechanical means, as for example, by printing or ruling adyeable substrate, for example, with a greasy ink formulation, inaccordance with the desired filter pattern, subjecting the substrate tosuitable coloration, in areas which do not possess the repellant inkmask, effecting removal of the mask, and repeating this procedure, inaccordance with the geometrical pattern of filter elements desired, asufiicient number of times to provide the desired multiplicity ofdiversely colored filter element; directly printing a carrier substratewith the desired dye formulations in accordance with the predeterminedfilter pattern and repeating this printing procedure a sufficient numberof times to provide the multiplicity of colored filter elements desired,or depositing, as an irregular filter screen pattern, a thin layercomprising a random distribution of small grains, such as starch grains,which have been independently colored with the colors desired foroptical filtering effects. Alternatively, color screen may be preparedby photomechanical methods of the type initially proposed by, forexample, Ducos Du Hauron in the nineteenth century, which comprise, ingeneral, coating a suitable support or film base with an adhesivecomposition having coated thereon a photosensitive colloid composition,as for example, dichromated gelatin, effecting exposure of the sensitivegelatin layer by incident actinic radiation, through a suitable maskwhich provides an exposure pattern devised in accordance with thedesired optical filter element arrangement, effecting differentialhardening of the sensitized material as a function of the point-to-pointdegree of exposure, removing unexposed unhardened material by solventcontact, subjecting the remaining hardened material to a suitable dyeingprocedure in order to provide a first-colored optical filter elementseries, and repeating this procedure, employing appropriate masks, asoften as necessary to provide the number of optical filter element typesdesired in the final color screen element.

Although color screen may be produced by traditional contact printing orprojection type photomechanical processes, a particularly preferredprocess for the production of color screen compirses the process setforth in US. Patent No. 3,284,208 which includes, in essence,successively coating the smooth surface of a lenticular film with aplurality of photoresponsive layers and sequentially subjecting thecoatings to selectively displaced radiation incident on, and focused by,the lenticules receiving same, in order to provide selective exposure ofthe coating. Subsequent to each exposure, unexposed coating is removedand the resultant resist dyed in order to provide a series of chromaticfilter elements, prior to the deposition of the next succeedingphotoresponsive layer. Each such exposure is derived fromelectromagnetic radiation incident on the lenticular film at an angulardisplacement specifically adapted to provide the desired plurality of 14chromatic filter element series in substantial side-by-side or screenrelationship and adapted to filter predetermined wavelengths of light.

For the preparation of the preferred trichromatic additive screens, theexposed area of each photoresponsive area will generally comprise aboutone-third of the layer contiguous each lenticule receiving exposingradiation. Although all three exposures may be accomplished by radiationincident on the lenticules of the lenticular film at three separateangles each adapted to provide exposure about one-third of the areacontiguous each lenticule receiving radiation, it will be recognizedthat the terminal chromatic filter formation may also be provided byexposing the terminal photoresponsive layer to diffuse radiationtraversing through the lenticular film and masked by the previouslyformed chromatic filter elements.

At a stage subsequent to formation of the first and second series offilter elements, the lenticular configuration will be constituted as acontinuous smooth surface. In the instances where the lenticulescomprise a separate stratum temporarily affixed to the surface of asupport on which the color screen is formed, such separate stratum maybe stripped from the support. Alternatively, where the lenticulescomprise an integral component of the film base or support and have beenprovided to the base by pressure and/ or solvent deformation of thebase, a continuous smooth surface may be reconstituted by application ofsuitable solvent and the deformation pressures produced during themanufacturing of lenticular film base released to provide reconstitutionof the bases original configuration. Where desired, for example, foroptical transmission purposes, the reconstituted surface may bepolished, for example, by surface contact with -an appropriate rotatingpolishing cylinder or drum, for the time interval necessary to providethe desired optical characteristics to the film base surface.

Optionally the external surface of the color screen may be overcoatedwith a protective polymeric composition, such as nitrocellulose,cellulose acetate, and the like, for the purpose of protecting thescreen from processing composition deformation during employment of theresultant film unit. The external surface of the color screen may thenhave applied thereto the remaining layers constituting the filmassemblage as detailed hereinbefore.

Apparatus particularly adapted to facilitate effecting exposure of thelenticular film in accordance with the aforementioned US. Pat. No.3,284,208 is disclosed and claimed in U.S. Pat. No. 3,318,220.

The support or film base employed may comprise any of the various typesof transparent ridged or flexible supports, for example, glass,polymeric films of both the synthetic type and those derived fromnaturally occurring products, etc. Especially suitable materials,however, comprise flexible transparent synthetic polymers such aspolymethacrylic acid, methyl and ethyl esters; vinyl chloride polymers;polyvinyl acetals; polyamides such as nylon; polyesters such as thepolymeric films derived from ethylene glycol terephthalic acid;polymeric cellulose derivatives such as cellulose acetate, triacetate,nitrate, propionate, butyrrate, acetate-butyrate, or acetate propionate;polycarbonates: polystyrenes; and the like.

The present invention will be illustrated in greater detail inconjunction with the following illustrative constructions which setforth representive embodiments and photographic utilizations of the filmunits of the present invention, which however, are not limited to thedetails therein set forth but are intended to be illustrative only.

The smooth surface of a lenticular film comprising a polyester film basemay have bonded to one surface a cellulose acetate butyrate layercomprising 550 lenticules per inch, each of which may possess aplano-convex configuration for condensing the incident radiation intoconverging rays and a focal length generally in the order of about 1 00microns in air and, as a result of this short focal length, imagingobjects over about one inch from the lens surface at infinity, may becoated on the opposite surface with an adhesive composition comprising70 cc. of methanol, 1.25 grams of nitrocellulose, and 30 cc. of butylalcohol. A first layer of gelatin sensitized by the addition of 15weight pecent potassium dichromate (based on dry gelatin), may then becoated on the external surface of the first adhesive layer. The firstgelatin layer may then be exposed to ultraviolet radiation, inaccordance with the previously detailed explanation, and the resultantphotoexposed carrier subjected to a water wash in order to provideremoval of unexposed sensitized gelatin, in accordance with the exposurepattern contained in the first gelatin layer. The web may then betreated with an acid dyeing bath comprising 1.17% Direct Red CI. 81;0.32% Direct Yellow Cl. 4; and 2.95% glacial acetic acid, rinsed toeffect removal of excess dye, dried and a second adhesive compositioncontaining 70 cc. of methanol, 30 cc. of butyl alcohol, and 1.25 gramsof nitrocellulose overcoated thereon. A second layer of gelatinsensitized by the addition of 15 weight percent potassium dichromate maybe coated on the second adhesive layer. The second photosensitizedgelatin layer may also be exposed to ultraviolet radiation in accordancewith the previously detailed description. The second gelatin layer maythen be washed with water to effect removal of unexposed photosensitivegelatin, in the manner previously detailed, and the remaining gelatinresist dyed by contact with an acid dyeing bath containing 0.83% AcidGreen Cl. 7; 0.32% Direct Yellow Cl. 4; and 2.86% glacial acetic acid.The web may then be rinsed to effect removal of any residual excess dye,dried and coated with a third adhesive composition comprising 30 cc.butanol, 1.25 grams of nitrocellulose, and 70 cc. of methanol. A thirdlayer of gelatin sensitized with 15 weight percent potassium dichromatemay then be coated on the external surface of the third adhesive layerand the third photosensitive gelatin layer subjected to exposure byultraviolet radiation, in accordance with the description detailedpreviously. The third layer of photosensitive gelatin may then be washedin order to provide the desired resist formation and the resultantresist dyed by contact with a solution containing 1.0% Blue T Pina and1% glacial acetic acid, washed to effect removal of residual dye anddried. A protective overcoat layer may be provided by coating theexternal surface of the multicolor screen element with a compositioncomprising 70 cc. methanol, 30 cc. butanol, and grams of nitrocellulose.

Subsequent to formation of the color screen, the lenticulated celluloseacetate butyrate may be removed from the polyester base and the externalsurface of the polymeric protective coating may be coated with acomposition comprising deacetylated chitin and copper sulfide at acoverage of about 4.4 mgs./ft. deacetylated chitin and 0.25 mg./ft.copper sulfide. On the external surface of the silver precipitatingagent containing layer may then be coated a hardened gelatino silveriodobromide emulsion coated at a coverage of 150 mgs./ft. gelatin and100 mgs./ft. silver and containing 7.4 mgs./ ft. propylene glycolalginate, 2.9 mgs./ft. sodium dioctylsulfosuccinate and an organogoldcomplex of the species and at the concentration identified below.

The gelatino silver iodochlorooromide emulsion employed may be preparedas previously detailed and chemically sensitized, at about 56 C., by theaddition of a sensitizing amount of a solution containng 0.1 gram ofammonium thiocyanate in 9.9 cc. of water and 1.2 cc. of a solutioncontaining 0.097 gram of gold chloride in 9.9 cc. of water. Theresultant emulsion may then be panchromatically sensitized by thesequential addition of 0.1%, by weight, methanol solutions of anhydro5,5- diphenyl-3,3'-bis-(4-sulfobutyl) 9-ethyloxacarbocyanine hydroxideand anhydro5,5-dimethyl-3,3-bis-(3-sulfopropyl)-9-ethy1-thiacarb0cyanine hydroxideis optionally effective concentrations.

The copper sulfide silver precipitating agent may be provided in situ bythe addition of substantially equimolar quantities of copper nitrate andsodium sulfide solutions to the deacetylated chitin coating soltuionprior to application of the composition to the color base support.

The film unit, fabricated either substantially as detailed above or inaccordance with any one or more of the structural embodiments denotedabove, may be subjected to exposing electromagnetic radiation incidenton the transparent base and developed by temporary contact of the filmunit, for about 60 seconds, with a processing composition, which forillustrative purposes may comprise 111 cc. of water, 0.36 gram oftriaminophenol, 6.0 grams of hydroxyethyl cellulose, 6.2 grams of sodiumhydroxide, 16 grams of sodium thiosulfate, 6.48 grams of sodium sulfite,0.42 gram of -nitrobenzimidazole, 7 grams of surfactant (reactionproduct of nonyl phenol and glycidyl), and 5 grams of tolylhydroquinone, to provide a positive silver image possessing the opticalcharacteristics described herein'before and the acuity required foradditive color reproduction.

For purposes of illustrating the advantageous results achieved by reasonof the present invention, film units, fabricated and processed in thegeneral manner detailed above, were subjected to an accelerated agenttest which comprised the exposure of processed units to an environmentaltemperature of 90 C., at a relative humidity of for one hour. Film unitsprepared with no organogold complex and possessing goldmercaptobenzimidazole complex disposed in the photosensitive silverhalide emulsion layer at ratios of 10.3/ 104 and 14.7/ 108.2, based uponthe ratio of gold to silver measured as elemental metal in mgs./ft.provided the statistical image stability results denoted below, intabular form, as Examples 1 to 3, respectively:

Example 1 l 2 3 Red D initial 3. 08 2.70 2. 92 Red D5151. test 2. l4 2.70 2.98 A D in percent Red 80. 0 0.0 +2 Green D L, initi 3. 62 3. 30 3.56 Green Dmnx test" 2. 84 3. 24 3. 50 A D in percent gree 19.0 1. 8 2.0Blue Draw... initial -4 8. 10 4 Blue rum, test; 2.96 3. 08 -4 A D inpercent blue -26. 0 1. 3 -0 1 113.6 In a/m Ag.

Repetition and extension of the last-identified test procedure for 72hours with respect to Examples 1 and 3, supra, provided the followingstatistical data:

Example 1 2 Red DML, initial 2. 92 3. 06 Red Dam, 1.64 2.70 A D inpercent red 44. 0 12. 0 reen Dina... initi 3. 48 3. 62 Green D1,, test.2. 32 3. 32 A D in percent green-. 33. 0 8.0 Blue Dmnx initial -4 -4Blue Du... test 2. 3. 76 A D in percent blue -28 -6 Example 1 1 2 7 3 45 6 Red Ding! initial. 3. 20 2.48 3.08 3.12 2.86 Red DmL, test... 2. 202.44 3.12 2.92 2. 82 A D in percent red 31.0 0 +1 3. 0 1. 4 Green Dmnxinitial. 3.82 2. 76 3. 72 3 60 2. 96 Green Dumb, St 2.92 2. 70 -4 2. 463. 08 A D in percent green 5. 5 24. 0 0.2 -+7 3. 1 +4.1

83 mgsJft. Ag. 2 118.6 rugs/It. Ag.

17 Repetition and extension of the last-identified test procedure for aperiod for 72 hours with respect to Examples 1, 2, 3 and 4, supra,provided the following statistical data:

Example 1 2 3 4 Red Da initial 2. 60 2. 70 2. 52 2.96 Red Dmtm, test-2.04 1. 30 2. 46 2. 58 A D in percent red- 21.0 52.0 2. O 13.0 Green DmB1,, initial- 2. 88 3.00 2. 86 3. 55 Green DML, test- 2.40 1. 88 2. 703.12 A D in percent gree 17. 37. 0 5. 5 12. 0 Blue Dmnx. 1m 2. 90 3. 262. 96 1 Blue Dmn!., 2. 72 2.50 2.90 3.44 A D in percent blue- 6.0 23.02. 0 -14. 0

'Film units were also fabricated and processed as last above with theexception that the processing composition comprised 2.2 grams of sodiumsulfite, 1.5 grams of sodium thiosulfate, 2.0 grams of the reactionproduct of nonyl phenol and glycidyl, 2.0 grams of tetramethyl reducticacid and 0.25 gram of diaminoorthocresol disposed in 50 cc. of acomposition comprising 111 cc. of Water, 6 grams of hydroxyethylcellulose and 6.25 grams of sodium hydroxide, the control unit comprised98.6 mgs./ft. silver as silver halide and the test unit comprised 12mgs./ft. gold as gold mercaptobenzimidazole and 115 mgs./ft. silver assilver halide. The film units thus fabricated and processed exhibitedinitial control and test silver transfer image Red D of 2.63 and 2.45and Green Dmax, of 3:16 and 3.01, respectively, which units uponexposure to conventional indoor lighting, under ambient temperature andhumidity conditions, provided the silver transfer image stability datagraphically illustrated in FIG. 1, wherein image density loss in percentis plotted as a function of time and the graphic data illustrated byCurves A, B, C and D represents, in order, the Red and Green D plots ofthe test and control units, respectively.

Film units were also fabricated and processed as first above with theexception that the processing composition comprised 0.18 gram of thetriaminophenol and the tolyl hydroquinone was replaced with dimethylhydroquinone and both the control and test units were exposed through aconventional step wedge to provide the graphic illustration of thecharacteristic curves of the respective silver transfer images set forthin FIG. 2. The detailed characteristic curves were determined byplotting the density of the respective images to blue, green and redlight, as a function of the log exposure of the photosensitive silverhalide emulsion, wherein Curves A, B, and C represent the characteristiccurves of the control film unit and Curves D, E, and F represent thecharacteristic curves of the test unit, the silver transfer image ofwhich had been contacted with a processing composition which comprised5.26 grams of gold thiosulfate and 1.02 grams of ethylene thiourea per100 cc. of water buffered at pH 9.0.

As will be expressly noted from examination of Curves A and D, the bluespeed of the test film unit read at 1.0 density comprises an ASA speedequivalent of 35, in comparison with the control unit which exhibits,under test conditions, an ASA speed equivalent of 22, two thirds of astop lower. The increase in blue speed thus obtained by means of thepresent invention specifically facilitates alleviation of the lack ofblue light output of conventional tungsten light sources, thusdecreasing the exposure filtration required to be employed for outdoorphotography to counteract the excess blue speed required for indoortungsten light illumination, commensurate with maintaining the blue,green and red speeds sensitometric balance required in each instance foracceptable photographic quality.

From the foregoing data it will also be readily noted that previouslydescribed significant improval in silver transfer image stability isdirectly achieved by means of the present invention when a silvertransfer image stabilizing concentration of a noble metal is employed asa constituent stabilizing component of a silver diffusion transferprocess system.

As denoted above, the photosensitive silver halide stratum and/or thesilver precipitating nuclei containing stratum may have advantageouslyincorporated therein discrete particulate materials providing increasedporosity to the film unit, without deleterious effect on the dimensionalstability of the binder lattice, in particular, those materials whichadditionally act as an antiswelling agent for the binder material and,accordingly, act to facilitate the prevention of the carried imagesmicroscopic distortion, particularly, with respect to an associatedcolor screen, such as discrete silica particles dispersed, for example,in a concentration of about 0.3 to 1.5 silica per part binder, for thepurpose of facilitating processing composition permeation of the filmunits silver halide crystals and silver precipitating nuclei containinglayer or layers. In addition, the silver halide or silver precipitatingnuclei containing stratum may be advantageously overcoated with aprocessing composition permeable polymeric material such as a hardenedgelatin pad or the like to advantageously promote uniformity inprocessing composition permeation of such stratum, by modulating anywave front resultant from initial surface contact with the liquidemployed and to thereby promote uniform maintenance of the polymericbinders physical characteristics.

Although chrome alum and particularly algin have been advantageouslyemployed as hardening agents for the polymeric gelatin emulsion binder,it will be recognized that substantially any hardening or crosslinkingagent may be employed, where necessary and with respect to any one ormore layers of the film unit, which does not provide deleteriousphotographic effects, to the extent required to provide a binder latticewhich eifectively inhibits to a substantial effect, migration of imagesilver. An extensive collection of hardening agents are disclosed in theart as specifically adapted to effect hardening or crosslinking ofphotographic polymeric binder material compositions and by reason oftheir innocuous photographic effects are to be be preferred in thepractice of the present invention. The sole requirement for effectiveoperation of the film unit is that the emulsions polymeric lattice beconstructed to provide the optical image parameters denotedhereinbefore. Thus, substantially any conventional hardening andcrosslinking agent may be selected from those set forth throughout, forexample, the pertinent patent literature regarding such agents, and theconcentration employed, as known in the art, will be dependent upon therelative activity of the selected agent, or agents, and the relativeamount of hardening or crosslinking to be effected. The specificconcentration of a selective hardening or cross-linking agent, to becontacted with a selected polymeric binder, may be readily determinedempirically, within the specific context of ultimate photographicemployment, by screening. It will be further recognized that any of thevarious processing composition permeable, synthetic or natural polymericmaterials, possessing the physical characteristics required to providethe results denoted above, may be substituted in replacement of thespecifically illustrated polymeric materials provided that such selectedpolymer provides a matrix which is not deleterious to photosensitivesilver halide crystals and possesses a lattice allowing processing inthe manner previously described.

Suitable silver halide solvents for employment in the practice of thepresent invention include conventional fixing agents such as thepreviously noted sodium thiosulfate, sodium thiocyanate, ammoniumthiocyanate, the additional agents described in US. Pat. No. 2,543,181,and the associations of cyclic imides and nitrogenous bases such asassociations of barbiturates or uracils and ammonia or amines and otherassociations described in US. Pat. No. 2,857,274.

Where desired conventional silver toning agent or agents may be disposedwithin the emulsion composition in a concentration effective to providea positive image toned in accordance with the desires of the operator.

In the preferred embodiment of the present invention, the processingcomposition will include an alkaline material, for example, sodiumhydroxide, potassium hydroxide or sodium carbonate, or the like, andmost preferably in a concentration providing a pH to the processingcomposition in excess of about 12. The processing composition may, wheredesired, contain the sole silver halide developing agent or agentsemployed, or a silver halide developing agent in addition to thatdisposed within the film unit; however, disposition of one or moredeveloping agents in the emulsion and/or a permeable layer directlyassociated therewith, intermediate the emulsion and a color screen, is aparticularly preferred embodiment, for the purpose of providing enhancedimage acuity, by more readily facilitating directly initiated development at radiation exposed areas of the emulsion without thenecessity of diffusing such agents to such sites by means of theprocessing composition selected.

The preferred silver halide developing agents generally comprise organiccompounds and, in particular, comprise organic compounds of the aromaticseries containing at least two hydroxyl and/or amino groups wherein atleast one of such groups is in one of ortho or para positions withrespect to at least one other of such groups such as, for example, thevarious known hydroquinones, p-aminophenols, and their various knownfunctional homologues and analogues.

It will be apparent that the relative proportions of the agentscomprising the processing composition set forth herein may be altered tosuit the requirements of the operator, however, the processingcomposition solvent employed will generally comprise water and willpossess a solvent capacity which does not deleteriously hydrate theselected binder lattices beyond that required to provide the preferredimage formation. Accordingly, no adjunct should be included within suchcomposition which deleteriously effects the lattice parameters requiredfor such image formation.

In the description herein, each color series of filter elements has beendescribed as covering that part of the total area in proportion to thetotal number of colors used, i.e., in the tricolor system, each coloroccupies one-third of the total area. This may vary quite widely beforehaving a noticeable effect to the observer and, in fact, may becompensated by changing the intensity of the colors. In actual practice,if one dye is of greater intensity than the others, a deliberatecompensation may be made by reducing the total relative area of theintense color. The aspect of relative areas is well known in the art sothat when relative areas are used in this application, it is intended toinclude the variances which the art would recognize as being successful.

Various colors and numbers of colors may be used in this invention butthe preferred system, as previously mentioned, is a tricolor arrangementof the three primary colors, red, green and blue.

It will be recognized, however, that, in accordance with the instantdisclosure, a plurality of chromatic filter element series may beprovided, the number of series being solely determined by the opticalparameters of the resultant color screen desired.

For example, a four-color system such as red, green, violet-blue andorange-yellow could also be effectively employed in accordance with theteachings of the instant disclosure.

In the practice of the present invention, additive trichromatic colorscreens possessing 550, 756, and 1125 triplets/inch may be readilyemployed and it has been found that image resolution obtained by meansof the present invention exceeds that obtainable in prior art processes.Such increased resolution specifically facilitates the acuity of colorreproduction to be achieved by the practice of the invention and thesilver halide stratum will be panchromatically sensitized to provideequal image production, as a direct function of incident exposingradiation, throughout the response portion of the radiation spectrum tofurther enhance the acuity of color information recordation by theemulsion.

In addition to the described essential layers, it will be recognizedthat the film unit may also contain one or more subcoats or layers,which, in turn, may contain one or more additives such as plasticizers,intermediate essential layers for the purpose, for example, of enhancingadhesion, and that one or more of the described layers may comprise acomposite of two or more strata which may be contiguous or separatedfrom each other.

Since certain changes may be made in the above product, process andapparatus without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A photographic silver diffusion transfer film unit which comprisesphotosensitive silver halide, silver precipitating nuclei, and asubstantially water-insoluble noble metal compound containing a noblemetal below silver in the Electromotive Force Series of Elements at aconcentration of at least about 1% by weight of noble metal based on theweight of silver present as silver halide.

2. A photographic silver diffusion transfer film unit as defined inclaim 1 wherein said noble metal compound comprises a substantiallywater-insoluble gold, platinum or palladium compound.

3. A photographic silver diffusion transfer film unit as defined inclaim 1 wherein said film unit comprises a laminate which includes acommon support carrying on one surface a layer comprising silverprecipitating nuclei and a layer comprising photosensitive silver halidecrystals.

4. A photographic silver diffusion transfer film unit as defined inclaim 3 wherein said noble metal compound is disposed in said layercontaining said photosensitive silver halide crystals.

5. A photographic silver diffusion transfer film unit as defined inclaim 3 wherein said laminate is a permanent laminate.

6. A photographic silver diffusion transfer film unit as defined inclaim 3 wherein said common support is transparent.

7. A photographic silver diffusion transfer film unit as defined inclaim 6 which includes an additive color screen intermediate saidtransparent common support and next adjacent essential layer.

8. A photographic silver diffusion transfer film unit as defined inclaim 1 wherein said concentration is effective to enhance stability ofa silver image provided by diffusion transfer processing of the filmunit.

9. A photographic silver diffusion transfer film unit which comprises aplurality of layers including a photosensitive layer containingphotosensitive silver halide and at least one substantiallyphotoinsensitive layer, at least one of said photoinsensitive layerscontaining a silver precipitating agent and at least one of saidphotoinsensitive layers including a substantially water-insoluble noblemetal compound containing a noble metal below silver in theElectromotive Force Series of Elements, at a concentration effective toenhance stability of a silver image provided by diffusion transferprocessing of the film unit.

10. A photographic silver diffusion transfer film unit as defined inclaim 9 wherein said noble metal compound is disposed in saidphotosensitive layer containing said silver precipitating agent.

11. A photographic silver diffusion transfer film unit as defined inclaim 9 which includes a common support and wherein saidphotoinsensitive layer containing said silver precipitating agent ispositioned intermediate said support and said photosensitive layercontaining said silver halide.

12. A photographic silver diffusion transfer film unit as defined inclaim 9 wherein said photosensitive layer containing said silver halideand said photoinsensitive layer contaning said silver preciptating agentare carried on separate supports.

13. A photographic silver diffusion transfer film unit as defined inclaim 9 wherein said film unit additionally includes a stripping layerintermediate said photoinsensitive layer containing said silverprecipitating agent and said photosensitive layer containing said silverhalide.

14. A photographic silver diffusion transfer film unit as defined inclaim 9 which includes a processing composition permeable layersubstantially devoid of silver halide and silver precipitating agent.

15. A photographic silver diffusion transfer film unit as defined inclaim 14 which includes a support and wherein said processingcomposition permeable layer is disposed intermediate said support and anext adjacent essential layer, said permeable layer having said noblemetal compound disposed therein.

16. A photographic silver diffusion transfer film unit as defined inclaim 13 which includes a support and wherein said processingcomposition permeable layer is disposed on the surface of the film unitmost distant from the support, said permeable layer having said noblemetal compound disposed therein.

17. A photographic silver diffusion transfer film unit as defined inclaim 9 wherein said silver precipitating nuclei are present in aconcentration effective to provide upon diffusion transfer processing ofthe film unit a silver image derived from unexposed silver halidecrystals possessing greater covering power than a silver derived fromexposed silver halide crystals.

18. A photographic silver diffusion transfer film unit as defined inclaim 9 wherein said noble metal compound is a substantiallywater-insoluble organometal compound of a noble metal below silver inthe Electromotive Force Series of Elements.

19. A photographic silver diffusion transfer film unit as defined inclaim 9 which includes an additive color screen.

20. A photographic silver diffusion transfer film unit which comprisesphotosensitive silver halide, silver precipitating nuclei and asubstantally water-insoluble noble metal compound at a concentrationeffective to enhance stability of a silver image provided by diffusiontransfer processing of the film unit, wherein said noble metal compoundpossesses the formula:

wherein M is a noble metal below silver in the Electromotive ForceSeries of Elements, and X is an organic ligand which provides asubstantially water-insoluble complex.

21. A photographic silver diffusion transfer film unit as defined inclaim wherein M is Au.

22. A photographic silver diffusion transfer film unit as defined inclaim 20 wherein M is An.

23. A photographic silver diffusion transfer film unit as defined inclaim 20 wherein X is an organic ligand containing a sulfur atom.

24. A photographic silver diffusion transfer film unit as defined inclaim 23 wherein X is a heterocyclic ligand containing said sulfur atom.

25. A photographic silver diffusion transfer film unit as defined inclaim 24 wherein X is mercaptobenzimidazole.

26. A photographic silver diffusion transfer film unit as defined inclaim 24 wherein X is l-phenyl-S-mercaptotetrazole.

27. A photographic silver diffusion transfer film unit as defined inclaim 24 wherein X is mercapto-N-methylimidazole.

28. A photographic silver diffusion transfer film unit which is apermanently fixed laminate and comprises a transparent support carryingon a first surface at least a first substantially photoinsensitive layercomprising silver precipitating nuclei, and at least a firstphotosensitive silver halide emulsion layer comprising photosensitivesilver halide crystals, and, associated with at least onephotoinsensitive layer of said film unit, a substantiallywater-insoluble noble metal compound of a noble metal below silver inthe Electromotive Force Series of Elements, said silver precipitatingnuclei present in a concentration effective to provide, upondevelopment, in the presence of a silver halide solvent, as a functionof exposure, a silver image derived from the development of exposedsilver halide crystals possessing a maximum image density at least 1.0density units less than the maximum density of silver image derived fromdevelop ment of unexposed silver halide crystals and said noble metalcompound present in a concentration effective to enhance the stabilityof said silver image derived from unexposed silver halide crystals.

29. A photographic silver diffusion transfer film unit as defined inclaim 28 wherein said film unit is a permanently fixed laminate andcomprises a transparent flexible polymeric support and carrying on afirst surface at least a first photoinsensitive layer comprising silverprecipitating nuclei dispersed in a processing composition permeablebinder, and at least a first photosensitive silver halide emulsioncomprising photosensitive silver halide crystals dispersed in aprocessing composition permeable binder, and, associated with at leastone processing composition permeable photoinsensitive layer of said filmunit, a substantially water-insoluble noble metal compound of a noblemetal below silver in the Electromotive Force Series of Elements, saidsilver precipitating nuclei present in a concentration effective toprovide, upon development, in the presence of a silver halide solvent,as a function of exposure of the unit to actinic radiation, a minimumsilver image density not in excess of about 0.5 and a maximum silverimage density of not less than about 1.5, and said noble metal compoundpresent in an effective silver image stabilizing concentration.

30. A photographic silver diffusion transfer film unit as defined inclaim 29 wherein at least one of said permeable polymeric binderscomprises gelatin.

31. A photographic silver diffusion transfer film unit as defined inclaim 28 which includes an additive color screen interposed intermediatesaid support and the next adjacent essential layer.

32. A photographic silver diffusion transfer film unit as defined inclaim 31 wherein said additive color screen comprises a trichromaticadditive color screen comprising red, green and blue filter elements ina screen pattern.

33. A photographic silver diffusion transfer film unit as defined inclaim 29 wherein said permeable binder of at least one of saidphotoinsensitive layers comprises deacetylated chitin.

34. A photographic silver diffusion transfer film unit as defined inclaim 28 wherein said noble metal compound is a substantiallywater-insoluble organometal compound of a noble metal below silver inthe Electromotive Force Series of Elements.

35. A photographic silver diffusion transfer film as defined in claim 34wherein said noble metal compound is gold mercaptobenzimidazole.

36. A photographic silver diffusion transfer film unit as defined inclaim 34 wherein said noble metal compound is gold1-phenyl-5-mercaptotetrazole.

37. A photographic silver diffusion transfer film as defined in claim 28wherein said photosensitive silver halide is panchromaticallysensitized.

38. A silver diffusion transfer photographic process which comprises, incombination, the steps of:

(a) exposing a photographic film unit comprising photosensitive silverhalide and silver precipitating nuclei;

(b) contacting said exposed film unit with a processing compositioncontaining a silver halide developing agent and a silver halide solvent,thereby providing a visible diffusion transfer process silver image tosaid unit, as a function of the poin-to-point degree of exposurethereof; and

(c) coacting said diffusion transfer process silver image within a noblemetal below silver in the Electromotive Force Series of Elements in aconcentration effective to enhance the stability of said silver image.

39. A silver diffusion transfer photographic process as defined in claim38 wherein said noble metal is initially disposed in said processingcomposition prior to contact of said composition with said film unit.

40. A silver diffusion transfer photographic process as defined in claim38 wherein said noble metal is disposed in said film unit prior tocontact of said unit with said processing composition.

41. A silver diffusion transfer photographic process as defined in claim38 which comprises, in combination, the steps of:

(a) exposing a film unit which comprises a permanent laminate whichincludes a support carrying on one surface a layer comprising silverprecipitating nuclei and a layer comprising photosensitive silverhalide;

(b) contacting the exposed silver halide layer with an aqueousprocessing composition containing a silver halide developing agent and asilver halide solvent thereby providing a visible silver image to saidfilm unit, in terms of the unexposed areas of said silver halide layer,as the function of the point-to-point degree of exposure thereof; and

(c) coacting said silver image with a noble metal below silver in theElectromotive Force Series of Elements in a concentration effective toenhance the stability of said silver image.

42. A silver diffusion transfer photographic process as defined in claim41 which comprises, in combination, the steps of:

(a) exposing a photographic film unit comprising a permanent laminatecontaining a transparent sup port carrying on a first surface asubstantially photoinsensitive layer comprising silver precipitatingnuclei, a photosensitive layer comprising photosensitive silver halidecrystals, and a noble metal below silver in the Electromotive ForceSeries of Elements;

(b) contacting the exposed silver halide layer with an aqueousprocessing composition containing a silver halide developing agent and asilver halide solvent for a period of time effective to provide avisible silver image to said film unit in terms of the unexposed areasof the photosensitive layer, as a function of exposure, and coactionbetween said silver image and said noble metal effective to enhance thestability of said silver image; and

(c) maintaining said laminate intact subsequent to processing.

43. A diffusion transfer color photographic process as defined in claim33 wherein said film unit includes a color screen and exposure of saidfilm unit is accomplished by radiation transmitted through said screen.

44. A diffusion transfer multicolor photographic proc ess as defined inclaim 43 wherein said color screen comprises a trichromatic additivecolor screen comprising red, green and blue optical filter elements in ascreen pattern.

45. A silver diffusion transfer photographic process as defined in claim38 wherein said noble metal is provided by a compound possessing theformula:

wherein M is a noble metal below silver in the Electromotive ForceSeries of Elements and X is an organic ligand which provides asubstantially water-insoluble complex.

24 46. A silver diffusion transfer photographic process as defined inclaim 45 wherein M is Au+ 47. A silver diffusion transfer photographicprocess as defined in claim 45 wherein M is An. 48. A silver diffusiontransfer photographic process as defined in claim 45 wherein X is anorganic ligand containing a sulfur atom.

49. A silver diffusion transfer photographic process as defined in claim48 wherein X is a heterocyclic ligand containing said sulfur atom.

50. A silver diffusion transfer photographic process as defined in claim49 wherein X is mercaptobenzimidazole.

51. A silver diffusion transfer photographic process as defined in claim49 wherein X is l-phenyl-S-mercaptotetrazole.

52. A silver diffusion transfer photographic process as defined in claim49 wherein X is mercapto-N-methylimidazole.

53. A silver diffusion transfer photographic process which comprises, incombination, the steps of:

(a) exposing a photographic film unit comprising photosensitive silverhalide, silver precipitating nuclei and a substantially water-insolublenoble metal compound containing a noble metal below silver in theElectromotive Force Series of Elements at a concentration of at leastabout 1% by weight of noble metal based on the weight of silver presentas silver halide; and

(b) contacting the exposed film unit with a processing compositioncontaining a silver halide developing agent and a silver halide solvent,to provide a visible silver image to said unit, as a function of thepointto-point degree of exposure thereof, and coaction between saidsilver image and said noble metal compound.

54. A silver diffusion transfer photographic process which comprises, incombination, the steps of:

(a) exposing a film unit which comprises a support carrying on onesurface a plurality of layers including a photosensitive layercontaining photosensitive silver halide and at least one substantiallyphotoinsensitive layer, at least one of said photoinsensitive layerscontaining silver precipitating nuclei, and at least one of saidphotoinsensitive layers having disposed therein a substantiallywater-insoluble noble metal compound of a noble metal below silver inthe Electromotive Force Series of Elements at a concen tration effectiveto enhance stability of a silver image provided by diffusion transferprocessing of the film unit;

(b) contacting the exposed silver halide layer with an aqueousprocessing composition containing a silver halide developing agent and asilver halide solvent thereby providing a visible silver image to saidfilm unit, in terms of the unexposed areas of said silver halide layer,as a function of the point-to-point degree of exposure thereof; and

(c) contacting said silver image with said noble metal compound.

60 55. A silver diffusion transfer photographic process as defined inclaim 54 which comprises, in combination, the steps of:

(a) exposing a photographic film unit comprising a permanent laminatecontaining a transparent support carrying on a first surface asubstantially photoinsensitive layer comprising silver precipitatingnuclei and a photosensitive silver halide layer comprisingphotosensitive silver halide crystals, and a substantiallywater-insoluble noble metal compound comprising a noble metal belowsilver in the Electromotive Force Series of Elements disposed in saidphotoinsensitive layer;

(b) contacting the exposed silver halide containing layer with anaqueous processing composition containing a silver halide developingagent and a silver halide solvent for a period of time effective toprovide a visible silver image to the silver precipitating nucleicontaining layer, as a function of exposure, and contact between saidsilver image and the noble metal compound; and

(c) maintaining said laminate intact subsequent to processing.

56. A silver diifusion transfer photographic process as defined in claim54 wherein the layer comprising said silver precipitating nuclei and thelayer comprising photosensitive silver halide are carried on separatesupports, including the step of separating said layers subsequent tocontacting said silver image with said noble metal.

References Cited UNITED STATES PATENTS NORMAN G. TORCHIN, PrimaryExaminer 10 J. L. GOODROW, Assistant Examiner U.S. Cl. X.R.

